Translucent sign

ABSTRACT

A translucent transit card advertising sign consisting of a sheet of paper or bristol of specific characteristics laminated between two sheets of plastic, one on each side of the paper or bristol. The paper or bristol has an opacity in the range between 90 and 96, a caliper of between 0.003 and 0.0065 inches, and a basis weight of between 120 and 240 pounds in the case of paper, and between 120 and 180 pounds in the case of bristol. When paper is used, its surface is clay coated. The plastic sheets each have a thickness of between 0.0015 and 0.005 inches. In some cases the plastic may be laminated only to one side of the paper or bristol and in that case the plastic thickness will be between 0.0015 and 0.010 inches.

United States Patent Goldman 1451 Nov. 28, 1972 15 1 TRANSLUCENT SIGN 3,312,563 4/1967 Rusch ..40/135 'x 72 Inventor: Allan Goldman, 23 v bank 3,402,495 9/1968 Fishback ..40/135 Crescent, Don Mills i 3,513,580 /1970 Agres ..40/135 x Canada Pnmary Examiner-Robert W. Michell [22] Filed: NOV- 14, 1969 Assistant Examiner-Richard Carter [21] APPL No; 876,807 Attorney-Rogers, Bereskin & Parr 57 ABSTRACT [52] US. Cl. ..40/135,40/132R [51] Int. Cl l/02 A translucent trans card advemsmg conslstmg [58] Field of Search /125 A 135 132 130 of a sheet of paper or bristol of specific characteristics 156/277 laminated between two sheets of plastic, one on each side of the paper or bristol. The paper or bristol has an opacity in the range between and 96, a caliper of [56] References Cited between 0.003 and 0.0065 inches, and a basis weight UNITED STATES PATENTS of between and 240 pounds in the case of paper, and between 120 and 180 pounds in the case of Myerson bristol' w p p used Surface is y coated. ,1 4,554 Gessler X The plastic Sheets each have a thickness f between 3,339,8 2": /1968 Deak ..40/ 135 UX 0.0015 and 0005 inches. In some cases the plastic 30l4828 g et a1 may be laminated only to one side of the paper or 3'389'036 6/1968 4 7 X bristol and in that case the plastic thickness will be b tw 0.0015 110.010 h 3,468,744 9/1969 Reinhart ..40/ 135 X e een me es 3,078,182 2/1963 Crone et a1. ..40/l35 UX 5 Clains, 3 Drawing Figures PATENTEDnnvza m2 3. 703,779

FIG] 6a 6b FIG. 3

INVENTOR. ALLAN GOLDMAN Byipyw, gwh. r?

TRANSLUCENT SIGN This invention relates to a novel type of sign or advertising poster suitable for use with back lighting.

There is presently a very large market for signs used in buses, streetcars, and subway trains in North America. These signs, commonly called transit cards, are usually displayed above the heads of passengers, and there is an increasing tendency to mount these signs in a position in which they are back lit, that is, the only lighting in the vehicle is located behind the transit cards and shines through them, so that the transit cards must be translucent. Such translucent transit cards have been used for a number of years and constitute a substantial portion of the total market for transit cards, but unfortunately, translucent transit cards have in the past been extremely expensive and difficult to produce.

The main reason why translucent transit cards have in the past been difficult and expensive to produce is that they must be made of relatively rigid material, so that they will have sufficient rigidity to retain their position in a card holder located above the passengers heads. The cardboard used to provide the rigidity for front lit signs cannot be used for back lit signs because such cardboard is not translucent, and therefore it has been the practise in the past to print the required imagery for back lit signs on plastic of about 0.020 inches in thickness. Usually the plastic is vinyl or polystyrene.

Considerable difficulty has been experienced in the past in obtaining good color fidelity of the advertised subject on translucent plastic transit cards. To explain this, a brief review of a typical color reproduction process will be helpful. In a conventional color reproduction process, the engraver prepares four individual .color separations of the art work being reproduced, by making four photographs of the art work through four filters, one for each color. The usual colors used for color separations are yellow, cyan (blue), magenta (red) and black. The engraver then rephotographs the resulting continuous tone negatives through screens at predetermined angles to obtain screened film positives.

After the film positives are complete, the engraver prepares proofing press plates, and from these plates he prepares progressive proofs (i.e., proofs made by the engraver). At the bottom of the progressive proofs are pure color solid (not screened) color bars used as an indicator of the amount of ink applied. The engraver examines the proofs to see if the colors are accurate, and he also takes readings of the color bars to see if the ink settings are in the range required by the printer who is eventually going to print the material on a production press. In North America the readings are normally in the printing taken by a conventional densitometer model RDlOO manufactured by the Macbeth Instrument Corporation, Newburg, N.Y. Such readings are called densichron readings. It can happen that the colors in the progressive proofs are accurate but that the densichron readings are not in the required range, in which case the printer would not be able to reproduce the material accurately on a production press (since he would be unable to match the ink readings). It can also happen that the densichron readings are in the required range but that the colors are not a faithful reproduction of those in the original artwork.

If the color bars of the progressive proofs yield densichron readings in the required range, but the colors in the progressive proofs are not faithful, then the engraver must return to his film and make color corrections. The engraver reduces or increases the size of dots in the areas of inaccurate color, and he then prepares new proofing press plates, and then new progressive proofs. As many as eight sets of proofing press plates and progressive proofs may be required before the colors are accurate with inks used in the required densichron reading range.

After film positives have been made that will yield faithful colors, the film positives are used to make final production press plates which are given to the printer, together with a final set of progressive proofs. The printer then prepares his press, building up the amount of ink used until his ink values yield color bars which are the same as those on the progressive proofs supplied to him. At this point the printed colors should be the same as those on the progressive proofs and hence should be accurate.

The progressive proofs prepared by the engraver are typically run off on a semi-automatic flat bed press or the equivalent, and this press is normally set up for paper, since most jobs undertaken by engravers are to be reproduced on paper. Even with an order for a given number of transit cards, normally half to three quarters of the order is usually printed on paper for mounting on cardboard to produce front lit signs, and only the remaining portion of the order is to be printed on plastic. To convert the press to produce progressive proofs on plastic would require changing all the inks used (since special inks are needed to print on plastic), in addition to ensuring that other conditions are suitable to enable printing on plastic. The cost of this procedure is so prohibitive that as a practical matter, progressive proofs on plastic for translucent printing cards are not economically feasible. Instead, the standard practise is simply to run the printing of the translucent plastic cards on the production press and hope for the best. The customer therefore never knows exactly what he is getting until the production press run has been completed. Since there is no way to determine how good the end result will be, and since often the color reproduction is not accurate, the customer is frequently unhappy and often will not use translucent transit cards as an advertising medium in the future.

In addition to the difficulties in obtaining accurate color reproduction for plastic, there are numerous difficulties at the production stage in simply printing on plastic. Firstly, plastic is non-porous, so that the ink lays on top and can take days to dry causing difficulty in handling the finished printed cards. Secondly, the unprinted plastic must be handled with gloves so that the oil on the workers fingers will not be transferred to the plastic, which would prevent ink adherence. Specially formulated inks must be used, the amount of fountain water transferred from the printing plate to the blanket of the offset press must be minimized during offset printing, a high ink fountain acidity must be maintained, cornstarch must be added to the ink to reduce the likelihood of the printed cards sticking together when stacked, and printing can be carried out on plastic during wet or rainy weather only with great difiiculty, because of the detrimental effects of high humidity.

A further problem is that the ink receiving characteristics of commercial vinyl and styrene sold for transit cards are not uniform, nor is the density, opacity and caliper uniform, thus aggravating the printing difficulties.

In addition it is difficult to determine what the color densities actually are on a plastic transit card after it has been printed,'because the densichron readings are distorted by the relatively great (0.020 inches) thickness of the plastic. Further, an adjustment of impression on the plates used to produce the paper transit cards for cardboard mounting must be made for the plastic printing, because of the different thickness of the material being printed. Moreover, it is often impossible to obtain sufficient color density simply by printing the plastic on one side, and it is necessary to back up the image by printing on the reverse side. Such double printing of the cards, which requires new film, new press plates, and accurate registration, is extremely expensive. Some printers have attempted to solve the problem by increasing the ink densities to the maximum possible extent, but this usually does not achieve the required color densities and often results in flooding or trapping of the ink, and in addition it results in almost complete loss of control of the colors, which can be highly undesirable'in many advertisements, particularly those involving foods.

The net result of the difficulties in producing back lit transit cards has been that potential buyers of the cards have been deterred both by their high cost and by their frequently inaccurate color reproduction, with the result that advertising spaces available for such cards have frequently gone unfilled.

The present invention provides a novel card or sign suitable for back lit illumination in which the difficulties of printing to obtain accurate color reproduction are substantially reduced and in which the cost is also reduced as compared with printing on the plastic cards previously used. According to the invention the image to be reproduced is printed on a sheet of paper of special characteristics, instead of on'plastic, and the paper is then laminated with plastic of specified thickness so that the resultant combination will have the required rigidity and yet will have the translucence necessary for proper light show through and color definition. The engraver can therefore see sample finished translucent sheets at the engraving stage, and he can modify the reproduction to suit the customer, all before the bulk press run. In addition, control of colors is greatly facilitated.

Further object and advantages of the invention will appear from the following disclosure, taken with the accompanying drawings, in which:

FIG. I is a sectional view of a portion of a transit card according to the invention, showing its construction;

FIG. 2 is a perspective diagrammatic view of a typical lighting fixture used in buses, subway cars and commuter railroad cars, showing a transit card in place on the fixture; and

FIG. 3 is a view similar to that of FIG. 1 but showing a transit card laminated only on one side.

As shown in FIG. 1, transit cards according to the invention are constructed by selecting a sheet of paper 2 of special characteristics to be described, printing the required imagery on the paper 2, and then laminating the paper 2 between two double layers 4, 6 of special plastic. The double layer sheet 4 consists of an inner layer 4a of polyethylene, and an outer layer 4b of polyester, normally that known under the trade mark Mylar. The polyethylene layer 4a is usually 0.0005 inches thick while the layer 4b of polyester is usually 0.001 inches thick, and the two are sold commercially as a single laminated sheet for use in laminating materials. In sheet 6, which is identical with sheet 4, reference 6a indicates the polyethylene layer and reference numeral 6b indicates the polyester layer.

The laminating process itself is conventional and consists of applying the sheets 4, 6 to the sides of the paper and subjecting the resultant sandwich to heat and pressure to form a lamination. During the lamination, the polyethylene layer melts and adheres to the surface of the paper to bond the plastic sheets to the paper over their entire area of contact, thus providing the required degree of rigidity. After the lamination has been completed, the edges of the resultant transit card are trimmed to the edge of the paper 2, thus exposing the edge of the paper to atmosphere. The exposed paper edge is so thin that the paper cannot absorb or lose any appreciable amount of moisture as the humidity in the atmosphere changes. Since the'humidity contect of the paper remains substantially constant, this means that the edges of the transit card will remain flat and will not wrinkle due to increases or decreases in the moisture content of the paper as the humidity of the atmosphere changes. For outdoor locations, the plastic will be trimmed to leave a plastic layer sealing the exposed paper edges, so that rain, dust, dirt, and grime cannot affect the paper.

It is preferred that the plastic be of a type which melts into the surface of the paper, because otherwise stability would be lost, and it might become necessary to make the plastic thicker, which would be undesirable since then too much diffusion of light would occur through the plastic.

Cards produced according to the invention are suitable for use in curved lighting fixtures of the form shown in FIG. 2. Such lighting fixtures-include a concavely curved front surface 10 and a pair of holder strips 12, 14 running horizontally along their top and bottom. A rectangular transit card, such as that shown at 16, is simply slipped into the lighting fixture with its upper edge retained by the upper holder strip 12 and its lower edge retained by the lower holder strip 14. The sides of the transit card are retained by a pair of resilient metal strips 18. Each strip 18 has its top and bottom ends held by the holder strips 12, 14, and each strip 18 is pushed into and remains in the curved configuration shown in which it presses the edges of the transit card 16 against the surface 10.

Transit cards as illustrated above are normally made in seven sizes in the United States, i.e., I 1X14, I 1X18, 11x21, 11x28, 11x42, 1 1X56, l l 84 (all dimensions are in inches). In all cases the material of the transit card should be sufficiently rigid so that the card will retain its inwardly curved configuration even at its unsupported center and not buckle outwardly, and the invention makes possible such cards.

Reference will next be made to the paper and printing requirements for the transit card illustrated in FIG. 1 and 2. The paper must be such that the completed laminated transit card will have sufficient translucency so that when it is back lit, the imagery thereon will appear sharp and with improved color fidelity. The opacity of the paper cannotbe too low, or the imagery will appear washed out, while if the opacity of the paper is too high, then the imagery will lack brilliance and the colors will appear dark. Opacity of paper is measured on an opacity scale of to 100, where 100 represents complete opacity, and 0 represents complete transparency. The opacity is commonly measured using a Bausch and Lomb opacimeter, or alternatively an opacimeter made by the General Electric Company and sold under the name GE Photovolt.

lt is found that on the opacity scale of 100, the opacity should be in a range between 90 and 96. If the opacity is less than 90, then it becomes difficult or impossible to obtain the required color density without printing the paper on both sides, which defeats the object of the invention, while if the opacity is greater than 9.6, insufficient light will pass through the transit card to illuminate the imagery thereon. The opacity figures given are for the paper before it is printed.

In addition, the caliper or thickness of the paper must fall within a specified range. If the paper is too thick, then it will diffuse the light passing through it to an undesirably high extent, and of course in addition, if the paper is too thick, normally the opacity will be too high. Conversly, if the paper is too thin, the finished product will lack stability and will not hold its position and configuration in a card holder. The lack of strength can be made up with extra plastic only to a limited degree, because if the plastic is made too thick, the light passing through it will be too greatly diffused, and sharpness and color fidelity will be lost. It is found that a caliper or thickness or between 0.003 and 0.0065 inches is suitable, and that higher or lower caliper are generally unsuitable. A preferred range for optimum results is 0.004 to 0.0055 inches. (It should be noted that the above mentioned caliper specifications are for the paper before it is printed. Printing will compress the paper by an amount dependent partly on the number of passes through the rollers of the printing press and partly on how well calendered the paper is. Ifthe paper is a bristol, its caliper may be reduced substantially, e.g., by about 0.0015 inches, during printing, while if the paper is coated and well calendered, its reduction in caliper will be negligible. Because the final caliper depends largely on the printing process and is variable, all calipers given here and in the appended claims are for paper before printing.)

Further, it is found that the basis weight of the paper is important. The basis weight (which is the weight of l,000 sheets of predetermined size) is generally an indication of the strength of the paper and is to some extend related to the caliper, although a paper can be thick and yet still be light and of low strength. The basis weight is also to some extent related to the opacity, in that the heavier the paper is, the more opaque it is likely to be, although there are many exceptions to this rule.

The size from which basis weight is computed varies depending on the type of paper. For example, for newsprint the basis weight is the weight of 1,000 sheets of size 24 by 36 inches; for tag paper the sheet size is 24 by 37 inches; for blotting paper the sheet size is 19 by 24 inches The present invention is concerned only with two kinds of paper, namely coated paper, and bristol. Coated paper is book or offset printing paper the surface of which has been coated with clay (on both sides of the paper) to improve its surface characteristics and translucency. The clay is a fine, powdery silicious material sometimes called China Clay or Kaolin. Bristol is a somewhat stronger material having longer fibers than printing paper, and may be coated or uncoated. For coated paper the basis weight is the weight of 1,000 sheets of size 25 by 38 inches, while for bristol the basis weight is the weight of 1,000 sheets of size 22% by 28% inches.

It is found that for coated papers, the basis weight should be between pounds and 240 pounds. A preferred range is pounds to 240 pounds. Below 160 pounds the paper strength is borderline, particularly for an 11 by 56 inch transit card, and the plastic laminations should be thickened slightly. It is found that the thickness of the combined layers of plastic lamination can be increased up to about 0.010 inches (i.e., a thickness of about 0.005 inches for each double sheet 4,6) without causing too much light diffusion, particularly for thinner papers. For bristol or other uncoated stock, thebasis weight should be between 120 pounds and pounds.

The selection of the paper or bristol to be used will depend largely on the image to be printed. On coated sheets color densities are greater but the fidelity of fine shades of half-tone is sometimes impaired. On uncoated sheets half-tones are improved, but the density of black areas is reduced. In addition uncoated sheets may show objectionable surface grain. A further factor is that for larger transit cards, e.g., of 11 by 56 inch size, it may be desirable to use stiffer paper or bristol than for the smaller sizes, e.g., 1 l by 21, unless thicker plastic is to be used for lamination. Thicker paper will, however, require greater ink densities, which may not always be desirable.

Once the paper has been selected, the ink, which should be of a non-bleeding variety, should be applied within specific densichron or densitometer ranges in order to provide proper color densities (and the press plates should be made such that accurate color reproduction will occur in these ranges). The required densitometer ranges are as follows:

It is found that if the amount of ink used is reduced to give densitometer readings below the lower limits in these ranges, then the colors will appear too washed out, while if the ink is increased to give densitometer readings above the upper limits in these ranges, then the colors will be too dark and strong. By way of example, printing was conducted on 160 pound coated enamel offset lithographic paper, using densitometer readings of 10 for the yellow, 12% for cyan, and 14% for the magenta, and acceptable results were produced.

With transit cards according to the invention, one set of production press plates'can be used for both back lit and front lit signs. The customer is given a final color proof before the production press plates are made, so that he will see how the finished printed work will appear, and also, the progressive proof can easily be laminated to duplicate exactly the appearance of the proposed completed translucent transit card. This gives the customer the opportunity to suggest changes at a stage at which they can be made. Then during the press run, the printer can print a given number of front lit transit cards and then continue his press run for back lit cards, using the same plates and the same paper, and

without the difficulties involved in printing on plastic. One precaution that should be taken during'printing, however, is that little or no offset spray should be used (this is a spray used to prevent the image on one sheet from transferring to the back of the adjacent sheet when the sheets are stacked). It is found that any offset spray remaining on a sheet during lamination will cause a starring effect on the finished product. Because little or no offset spray should be used, the printed sheets should be stacked only in small piles after they emerge from the press.

It is also found that the finished laminated transit cards have an anti static property when a polyester outer sheet is used for laminating, i.e., they do not attract dust, and dirt as readily as do vinyl and styrene translucent transit cards. This eliminates the need for waxing the translucent transit cards laminated using polyester, whereas conventional vinyl and styrene translucent transit cards must be waxed periodically to prevent adherence of dust and dirt.

Although it has been assumed that transit cards according to the invention are to laminated with plastic on both sides, they can if desired be laminated only on one side. A typical portion of a transit card laminated on one side only is shown in FIG. 3, where primed reference numerals indicate parts corresponding to those of FIG. 1. Lamination on one side only is, however, less desirable than lamination on two sides, because unless heavier plastic is to be used, relatively thick paper or bristol (e.g., 0.0065 .inches in caliper) must be used to provide sufficient stability. Because of the thicker paper and consequent greater diffusion of colors when back lit, greater color densities must be provided during printing, or else slightly reduced color quality must be accepted as compared with that obtainable on thinner papers. in addition, of course, the card is more subject to deterioration since it is protected only on one side.

It is found that bristol of 0.0065 inch caliper when laminated on one side only with a 0.0015 inch layer 4 of polyethylene and polyester, has sufficient stability for the l l by 28 inch size transit card. For larger sizes,

the plastic thickness should be increased and can be increased up to a maximum of about 0.010 inches. Above this thickness, the light diffusion through the plastic is objectionable.

It will be appreciated that the invention is applicable to black and white signs, and two and three color signs, as well as to four color signs.

What I claim as my invention is:

l. A translucent sign for a curved back-lit sign holder of a transit vehicle, said sign being 'of elongated rectanular sha and com risin a sheet of a r havin oth its sfd es coated zvith lay, said pap r aving ar i opacity of between 90 and 96 before printing, a basis weight of between 160 and 240 pounds, a thickness of between 0.003 and 0.0065 inches before printing, an image printed on one side only of said sheet of paper, said sheet of paper being-laminated between a pair of plastic sheets, the thickness of each of said plastic sheets being between 0.0015 and 0.005 inches, said plastic'sheets being fused into and adhered to said sheet of paper over substantially their entire area of contact with said sheet of paper, so that said sign will retain a curved configuration when it is inserted into said curved sign holder.

2. A sign according to claim 1 wherein said image is a lithograph image.

3. A sign according to claim 2 wherein said sign is l 1 inches in one dimension and between 14 and 84 inches in its other dimension.

4. A sign according to claim 2 wherein said image is formed by inks of colors selected from yellow, cyan, magenta and black, said yellow having a color density in the densichrometer range 9 to 13, said cyan having a color density in the densichrometer range 1 1% to 15, and said magenta having a color-density in the densichrometer range 13 to 17.

5. A rectangular translucent transit sign for a curved back-lit sign holder of a transit vehicle, said sign comprising a sheet of bristol having an opacity of between 90 and 96 before printing, a basis weight of between 120 and 180 pounds, a thickness of between 0.003 and 0.0065 inches before printing, a lithographic image on said sheet, said image being fonned by .inks of colors selected from yellow, cyan, magenta and black, said 

1. A translucent sign for a curved back-lit sign holder of a transit vehicle, said sign being of elongated rectangular shape and comprising a sheet of paper having both its sides coated with clay, said paper having an opacity of between 90 and 96 before printing, a basis weight of between 160 and 240 pounds, a thickness of between 0.003 and 0.0065 inches before printing, an image printed on one side only of said sheet of paper, said sheet of paper being laminated between a pair of plastic sheets, the thickness of each of said plastic sheets being between 0.0015 and 0.005 inches, said plastic sheets being fused into and adhered to said sheet of paper over substantially their entire area of contact with said sheet of paper, so that said sign will retain a curved configuration when it is inserted into said curved sign holder.
 2. A sign according to claim 1 wherein said image is a lithograph image.
 3. A sign according to claim 2 wherein said sign is 11 inches in one dimension and between 14 and 84 inches in its other dimension.
 4. A sign according to claim 2 wherein said image is formed by inks of colors selected from yellow, cyan, magenta and black, said yellow having a color density in the densichrometer range 9 to 13, said cyan having a color density in the densichrometer range 11 1/2 to 15, and said magenta having a color density in the densichrometer range 13 to
 17. 5. A rectangular translucent transit sign for a curved back-lit sign holder of a transit vehicle, said sign comprising a sheet of bristol having an opacity of between 90 and 96 before printing, a basis weight of between 120 and 180 pounds, a thickness of between 0.003 and 0.0065 inches before printing, a lithographic image on said sheet, said image being formed by inks of colors selected from yellow, cyan, magenta and black, said yellow having a color density in the densichrometer range 9 to 13, said cyan having a color density in the densichrometer range 11 1/2 to 15, and said magenta having a color density in the densichrometer range 13 to 17, said sheet of bristol being laminated between a pair of plastic sheets, the thickness of each of Said plastic sheets being between 0.0015 and 0.005 inches, said plastic sheets being fused to and adhered to said sheet of bristol over said substantially their entire area of contact with said sheet of bristol. 